React State Management

const [state, setState] = useState(initialValue); # declare state
setState(newValue); # update state
setState(prev => prev + 1); # functional update

const [name, setName] = useState("John");
const [age, setAge] = useState(30);
const [isActive, setIsActive] = useState(true);

const [user, setUser] = useState({ name: "John", age: 30 });
setUser({ ...user, age: 31 }); # update property
setUser(prev => ({ ...prev, age: 31 })); # functional

const [items, setItems] = useState([]);
setItems([...items, newItem]); # add item
setItems(items.filter(i => i.id !== id)); # remove item
setItems(items.map(i => i.id === id ? updated : i)); # update item

class Counter extends React.Component {
    state = { count: 0 }; # initialize state
    this.setState({ count: 1 }); # update state
    this.setState(prev => ({ count: prev.count + 1 })); # functional
}